Method for manufacturing a frame for an electric motor

Abstract

A method for manufacturing a frame for an electric motor including a frame main body and a metallic member welded to the outer surface of the frame main body is disclosed. After metallic members such as cooling fins are attached to the outer surface of a hollow cylindrical frame main body by projection welding which results in distortion of the frame main body due to radial expansion, sizing is applied to the inner surface of the frame main body by applying a radially outward force from inside of the frame main body to remove the distortion and expand the frame main body so that the inner surface of the frame main body defines a true circle.

What is claimed is: 
     
       1. A method for manufacturing a frame for an electric motor including a frame main body comprising the steps of: preparing a hollow cylindrical frame main body of a circular cross section;   preparing a plurality of metallic elongated cooling fins to be welded to the frame main body;   attaching said plurality of cooling fins to the outer surface of said frame main body by projectionwelding, which results in distortion of the frame main body due to radial expansion during the projection welding; and   sizing the inner surface of said frame main body by applying a radially outward force thereto from inside said frame main body to expand the frame main body so as to remove the distortion and produce, by plastic expansion, a greater percent radial expansion of the inner surface of the frame main body than the mean percent radial expansion of the inner surface of the frame main body due to the distortion during projection welding, and an inner surface of said frame main body in the form of a true circle.   
     
     
       2. A method for manufacturing a frame for an electric motor as claimed in claim 1 wherein said metallic member is an elongated cooling fin having substantially a U-shaped cross section. 
     
     
       3. A method for manufacturing a frame for an electric motor as claimed in claim 1 wherein said frame main body is formed by seam welding the longitudinal joint of a metallic sheet rolled into a cylinder. 
     
     
       4. A method of manufacturing a frame for an electric motor as claimed in claim 1 wherein said step of sizing the inner surface of said cylindrical frame main body comprises plastic forming by a plurality of expansion pawls. 
     
     
       5. A method for manufacturing a frame for an electric motor including a frame main body and a stator core comprising the steps of: preparing a hollow cylindrical frame main body of a circular cross section;   preparing a plurality of metallic elongated cooling fins to be welded to the frame main body;   attaching said plurality of cooling fins to the outer surface of said frame main body by projection welding, which results in distortion of the frame main body due to radial expansion during the projection welding;   sizing the inner surface of said frame main body by applying a radially outward force thereto from inside said frame main body to expand the frame main body, by plastic expansion, so as to remove the distortion and produce an inner surface of said frame main body in the form of a true circle; and   press-fitting the stator core into the frame main body by elastic expansion so that the outer circumferential surface of the stator core is brought into intimate contact with the inner circumferential of the frame main body.